The running speed of the traditional automotive alternator pulley is synchronized with the car engine. If the speed of the engine changes, the speed of the alternator changes accordingly. The output torque and speed of an internal combustion engine are acyclic due to the explosion of the cylinders. Especillay, when the engine is suddenly accelerated or decelerated, the speed of the alternator pulley changes. However, due to the alternator effect inertia rotor, the rotor speed of the alternator is synchronized with the speed of the engine suddenly. The impact will be formed between the belt and the pulley, reducing belt life and producing noise, resulting an engine Front End Accessory Drive (FEAD). Especially, before the engine is stopped, the engine crankshaft has a short positive and negative direction swing. The excitation coil in the rotor causes damage and reduces the life of the alternator by centrifugal force.
To improve the life of the engine and FEAD, an improvement is made on the structure of the pulley. Such as, Chinese patent application No. CN200920294667 discloses a Overrunning Alternator Pulley (OAP). The OAP includes a pulley wheel, a pulley shaft, an upper ball bearing and lower ball bearing located between the pulley wheel and the pulley shaft, and a overrunning clutch that is arranged between the upper ball bearing and the lower ball bearing. However, the structure of the above overrunning pulley is complicated. It has only overrunning function but no damping function.